Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 163-170).

A new and improved stabilizer was developed for the variable speed generation (VSG) system. The VSG system exhibits periodic oscillations which sometimes leads to a loss of synchronism. After careful study, a simple but effective strategy to stabilize the system was implemented with real time digital feedback control. The VSG system consists of an engine, which is the prime mover, driving a doubly fed machine (DFM), which is the generator. The stator of the DFM is directly connected to the grid while the rotor is connected to the grid through a power electronic converter. The converter used in this study is a series resonance converter (SRC), but the proposed method may also be applied to other kinds of converters. The stabilizer senses the RPM of the engine, the feedback signal, and controls the rotor current amplitude and frequency of the doubly fed machine. Control was implemented using the 80C196KB microcontroller. The software consists of a mix of "C" and assembly language. Speed being an important factor in the implementation, care was taken to minimize the control loop times. The important features of the hardware and software developed for the stabilizer are: (1) 12 MHz controller board (2) Real time digital band pass filter (3) Instantaneous rotor speed measurement (4) Interrupt driven measurement and control loops (5) User defined setup parameters (6) IBM PC based real time serial communication The performance of the VSG system was studied with and without the stabilizer. A significant improvement in the stability of the system was noticed over the entire region of operation. / Graduation date: 1991

A motor drive consisting of two parallel voltage-sourced converters was developed and implemented. A parallel converter arrangement allows the system to be constructed in a modular fashion to gain economies of scale and redundancy. The converters are connected to common ac- and dc-buses without isolation and are controlled without inter-converter communication or a master/slave arrangement. The system was simulated and the results validated against an experimental setup. Both steady-state and dynamic load sharing were achieved through the use of drooped PI speed regulators. PI controllers were used to regulate the quadrature currents provided by each converter. Circulating 0-sequence current was regulated using P controllers. A linearized state-space model of the system was developed and an eigenvalue analysis was performed, showing system stability. Speed steps in simulation and in the laboratory demonstrated good response. The loss of one converter’s gating was emulated. The system continued to operate, showing an advantage of system redundancy.

A motor drive consisting of two parallel voltage-sourced converters was developed and implemented. A parallel converter arrangement allows the system to be constructed in a modular fashion to gain economies of scale and redundancy. The converters are connected to common ac- and dc-buses without isolation and are controlled without inter-converter communication or a master/slave arrangement. The system was simulated and the results validated against an experimental setup. Both steady-state and dynamic load sharing were achieved through the use of drooped PI speed regulators. PI controllers were used to regulate the quadrature currents provided by each converter. Circulating 0-sequence current was regulated using P controllers. A linearized state-space model of the system was developed and an eigenvalue analysis was performed, showing system stability. Speed steps in simulation and in the laboratory demonstrated good response. The loss of one converter’s gating was emulated. The system continued to operate, showing an advantage of system redundancy.

The PWM (pulse-width-modulated) type voltage source converters (VSC) allow a precise speed control of induction motors with maximum achievable energy efficiency. However, the rapid growth of this technology has created quite a concern, as the PWM waveform produces complex transients that stress the motor insulation, to much severe levels, compared to the normal sinusoidal voltage waveforms. As a result, the machine may fail prematurely due to increased dielectric heating; high turn-to-turn stress caused by non-linear potential distributions; increased partial discharge (PD) activities due to overshoots in pulse waveforms; and built-up space charge by high frequency signals. The present work therefore addresses the problems associated with enamelled wires and groundwall insulation in motor stator coil working under PWM-VSC.

The PWM (pulse-width-modulated) type voltage source converters (VSC) allow a precise speed control of induction motors with maximum achievable energy efficiency. However, the rapid growth of this technology has created quite a concern, as the PWM waveform produces complex transients that stress the motor insulation, to much severe levels, compared to the normal sinusoidal voltage waveforms. As a result, the machine may fail prematurely due to increased dielectric heating; high turn-to-turn stress caused by non-linear potential distributions; increased partial discharge (PD) activities due to overshoots in pulse waveforms; and built-up space charge by high frequency signals. The present work therefore addresses the problems associated with enamelled wires and groundwall insulation in motor stator coil working under PWM-VSC.

Thesis--Universität München, 2007. / Includes bibliographical references.

This thesis presents a detailed comparison of the torque-speed characteristics of three permanent magnet synchronous machine designs based on how the magnets are mounted. The machines investigated are an interior permanent magnet machine, an interior-rotor surface-mounted machine and an exterior-rotor surface-mounted machine. They are designed for traction drives in hybrid electric vehicles. Two sets of comparisons based on the same machine volume and starting torque are performed. Important issues, such as machine mass and cost, cogging torque, and flux-weakening capability are addressed. Computer simulations were performed to estimate their performances and the results are presented. Design guidelines and tradeoffs of their performances are extracted from the simulation results. Relative strengths and limitations of different PM machine types are highlighted.

This thesis describes work that has been carried out to develop a scaled down laboratory test bed for use in the optimisation of fan driven air ventilation systems found at the various Anglo Coal South African mines. The present system involved in the movement of air underground comprises a fixed speed centrifugal fan driven damper controlled system. National Power Contractors (NPC) together with the University of KwaZulu-Natal (UKZN) proposed a variable speed automated controlled system, but the costs of installing Variable Speed Drives (VSD) and their impact on the energy consumption of a system prior to being installed are important. In addition deliverables required by the industrial partner NPC was to develop a calibrated simulation model where any fan system could be simulated showing potential energy savings. A test bed was therefore constructed to evaluate the power usage of a VSD while driving a simulated fan. The test bed comprised of two Field Oriented Controlled induction machines. A ventilation system at Anglo Coal’s Vlaklaagte colliery was proposed to be simulated by the test bed to develop the Measurement and Verification (M&V) methodology required to represent a business case, but since data from this fan system was not available two other fan systems were studied. One fan system was built at the UKZN whilst the other industrial fan system was at Anglo Coal’s Greenside colliery. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

There is an apparent disagreement between recent commentators who find in Nietzsche both a constructive philosophy and a compatibilist account of freedom, and Brian Leiter’s reading that rejects both. The reason for this disagreement, I argue, is that Leiter’s “illiberal” view is limited in scope to Nietzsche’s critical philosophy, while Nietzsche also has a constructive philosophy aimed at select readers. I read Nietzsche’s critical philosophy as targeting the metaphysical entities that underpin asceticism and herd values, not the mental states and processes with which these entities are associated. The “no such entity” reading preserves the resources needed to read Nietzsche as offering a replacement for the ascetic ideal—and an alternative source for life’s meaning. Although few of his readers will have been born with the drives needed to throw off herd values and enjoy compatibilist freedom, these readers are the intended audience for Nietzsche’s constructive philosophy.